How can I loop animation in Blender through Viewer Node
If you already rendered the animation, you can use Blender Video Sequence Editor. Just add clip with the animation and duplicate it as many times you need.
If you want to render already looped animation you can use NLA Editor. Just switch Dope Sheet to Action Editor and click on Push Down to move the animation to NLA Editor. Then switch to NLA Editor and from there you can select the strip and set Repeat in Playback Settings on the right tool shelf, to whatever number you need.